Method and apparatus for reporting channel state information in a wireless communication system

ABSTRACT

A method and apparatus are provided for reporting Channel State Information (CSI) in an uplink by a User Equipment (UE) in a wireless communication system. The method includes reporting a first Precoding Matrix Indicator (PMI) to an evolved Node B (eNB); calculating a second PMI using the first PMI; and reporting the second PMI to the eNB.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.13/645,082, which was filed in the United States Patent and TrademarkOffice on Oct. 4, 2012, and claims priority under 35 U.S.C. §119(e) toU.S. Provisional Application No. 61/543,016, which was filed in theUnited States Patent and Trademark Office on Oct. 4, 2011, the entiredisclosure of each of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method forreporting Channel State Information (CSI) in a wireless communicationsystem, and more particularly, to an apparatus and method for reportingCSI for a stable operation of a network in a situation where a PrecodingMatrix Indicator (PMI) and a Channel Quality Indicator (CQI) cannot becalculated.

2. Description of the Related Art

In the 3^(rd)-Generation Partnership Project (3GPP) Radio Access Network1 (RAN1), there are various feedback report modes for CSI a UserEquipment (UE) feeds back with respect to a downlink channel state to anevolved Node B (eNB). The CSI is used for scheduling a downlink channelin the eNB.

Basically, there are two CSI reporting channels for a feedback report ofthe CSI; (1) a Physical Uplink Control Channel (PUCCH), and (2) aPhysical Uplink Shared Channel (PUSCH). The CSI report is classifiedinto a periodic CSI report and an aperiodic CSI report, and the periodicCSI report is done via the PUCCH and the aperiodic CSI report is done bythe PUSCH.

The CSI, as is well known, includes at least one of a Rank Indicator(RI), a Precoding Matrix Indicator (PMI), and a Channel QualityIndicator (CQI). The RI indicates the number of ranks of a channel,i.e., the number of layers to be used for downlink transmission. The PMIincludes information about a precoding matrix desired to be used fordownlink transmission. The PMI is based on the number of layersindicated by the RI. The CQI indicates a modulation scheme and a coderate desired to be used for downlink transmission.

Further, the CSI report may be classified into a wideband reportreflecting a state of a total cell bandwidth and a subband reportreflecting a state of each subband.

Referring to the standard documents, i.e., 3GPP TS 36.211 v10.3.0 and3GPP TS 36.213, v10.3.0, there are a plurality of modes for CSIreporting in the PUCCH, and among the plurality of modes, referring toPUCCH mode 2-1, when the transmission mode 9 with 8 CSI-RS isconfigured, the wideband/subband PMI and wideband/subband CQI arereported on a specific reporting time instance. The selected precodingmatrix is selected by two PMIs, i.e., a first PMI and a second PMI.

The PMIs information and a single precoding matrix for a correspondingrank are selected according to a codebook, which is defined in Table6.3.4.2.3-3 to 6.3.4.2.3-10 in the 3GPP TS 36.211 v10.3.0. The PMIs andthe CQIs are calculated based on the last reported RI.

However, according to conventional standard techniques in associationwith calculation of the PMI and the CQI, the PMI and the CQI cannot becalculated in certain cases. In these cases, stable communicationbetween a network and a UE cannot be guaranteed. More specifically, thewideband first PMI value is calculated based on the last reportedperiodic RI. The wideband or subband PMI is calculated based on the lastreported periodic RI and the wideband first PMI. The wideband or subbandCQI value is calculated based on the selected precoding matrix and thelast reported periodic RI. When a reported RI is changed and the nextcoming report is a second PMI and CQI, there is no first PMI that iscalculated based on the last reported RI. In this case, the second PMIand CQI value cannot be calculated. Therefore, a need exists for ascheme that provides stable communication between a network and a UEwhen the PMI and the CQI cannot be calculated.

SUMMARY OF THE INVENTION

Accordingly, the present invention is designed to address at least theproblems and/or disadvantages described above and to provide at leastthe advantages described below.

An aspect of the present invention is to provide a method and apparatusfor reporting CSI for stable operation of a network when a PMI and a CQIcannot be calculated in a wireless communication system.

In accordance with an aspect of the present invention, a method isprovided for reporting CSI in an uplink by a UE in a wirelesscommunication system. The method includes reporting a first PMI to aneNB; calculating a second PMI using the first PMI; and reporting thesecond PMI to the eNB.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an improper first PMI, when a second PMI and a CQIare calculated after an RI is changed in a wireless communicationsystem;

FIG. 2 illustrates an improper first PMI, when a second PMI and a CQIare calculated after an RI and a Precoding Type Indicator (PTI) aresimultaneously changed in a wireless communication system;

FIG. 3 illustrates an improper first PMI, when a second PMI and a CQIare calculated after an RI is changed in a wireless communicationsystem;

FIG. 4 illustrates a method for calculating a second PMI based on aprevious RI condition according to an embodiment of the presentinvention; and

FIG. 5 is a block diagram illustrating a UE according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, specific details such as detailed configuration andcomponents are merely provided to assist the overall understanding ofthese embodiments of the present invention. Therefore, it should beapparent to those skilled in the art that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of the present invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

In the embodiments of the present invention described below, a PMIincludes a first PMI and a second PMI, which correspond to a dualcodebook structure defined in a Long Term Evolution-Advanced (LTE-A), asproposed in the 3GPP. The first PMI indicates a precoding matrixindicator in a wideband and long-term channel condition. The second PMIindicates a precoding matrix indicator in the wideband channel andlong-term channel condition according to a Precoding Type Indicator(PTI) value which a User Equipment (UE) feeds back and an instance atwhich feedback information is reported, or a precoding matrix indicatorin a subband and short-term channel condition.

For example, in PUCCH mode 2-1, according to a PTI value fed back by theUE, if PTI the UE feeds back most recently is 0, then the second PMIindicates wideband channel information; if the most recently fed backPTI is 1, then the second PMI indicates wideband channel information orsubband channel information according to an instance at which thefeedback transmission is performed.

Additionally, in FIGS. 1-4, “WB W 1” indicates a first PMI of awideband, “WB W2” indicates a second PMI of a wideband, “WB CQI”indicates a wideband CQI, “RI” indicates the rank indicator, and a “PTI”has a value of “0” or “1”. For example, in the transmission mode 9 with8 CSI-RS, a PMI and a CQI are calculated in different ways.

FIG. 1 illustrates an improper first PMI, when a second PMI and a CQIare calculated after an RI is changed in a wireless communicationsystem. Specifically, in FIG. 1, reference numerals 101 through 109refer to instances at which corresponding CSIs are reported.

Referring to FIG. 1, an RI of “1” at 101 is changed to “2” at 105, andas the RI is changed at 105, a second PMI (WB W2) and a CQI (WB CQI) ofa wideband are reported at 107. In this case, a first PMI and an RI lastreported before reporting of the second PMI and CQI (WB W2, WB CQI) at107 are the first PMI (WB WB1) reported at 103 and the RI reported at105. However, the first PMI reported at 103 becomes invalid when the RIis changed at 105. Accordingly, because the first PMI reported at 103 isnot valid after changing the RI at 105, it is not clear how the secondPMI and the CQI at 107 and 109, respectively, are calculated based onthe now invalid first PMI reported at 103.

FIG. 2 illustrates an improper first PMI, when a second PMI and a CQIare calculated after an RI and a PTI are simultaneously changed in awireless communication system. Specifically, in FIG. 2, referencenumerals 201 through 209 refer to instances at which corresponding CSIsare reported.

Referring to FIG. 2, when an RI and a PTI are changed at the same timeat 201, the following second PMI and CQI have an improper first PMI,which is supposed to be calculated at 201 based on the last reported RI.Therefore, not only a wideband second PMI and a wideband CQI value at203, but also sequential subband PMI and subband CQI values reported at205, 207, and 209 are calculated without the proper first PMIinformation.

FIG. 3 illustrates an improper first PMI, when a second PMI and a CQIare calculated after an RI is changed in a wireless communicationsystem.

Referring to FIG. 3, when an RI is changed at 303, then the followingwideband second PMI and wideband CQI are supposed to be calculatedconditioned on the last reported first PMI at 301. However, the RIassumption of the first PMI at 301 and the RI assumption of the secondPMI at 305 are different. Therefore, it is also not clear how tocalculate the second PMI and CQI at 305. This is similar to the caseillustrated in FIG. 1.

The above-described examples where a calculation of the second PMI andthe CQI become unclear are addressed in various manners by variousembodiments of the present invention, as described below.

Embodiments of the present invention described below assume that in thetransmission 9 with 8 CSI-RS ports, the feedback reporting includes thefirst and second PMI in accordance with the dual codebook structure,which was agreed in Release 10 of the 3GPP LTE standard.

The first PMI represents the wideband and long-term channel conditions.The second PMI represents the subband or short-term channel conditions.If a channel is not changed rapidly, then even though the rank changes,it does not change dramatically.

For example, when an RI starts as 1, it could change to 2. In this case,the wideband/long-term channel condition would not change that much.Therefore, it is possible that the same wideband/long-term channelcondition is fedback to a network. In particular, according to acodebook structure of an 8 CSI-RS port, the first PMI of Rank 1 and Rank2 are the same in the context of a codeword and the index of thecodeword. The same condition holds in Ranks 3 and 4.

Additionally, the first PMIs of Ranks 5, 6, and 7 are the same.Therefore, when RI changes from Rank 1 to Rank 2 or vice versa, thenthere is a high probability to indicate the same first PMI. In thiscase, the first PMI may be re-used to calculate the second PMI and theCQI. The same first PMI in the changed RI can be used to calculate thesecond PMI and CQI when a rank is changed between Ranks 1 and 2, orbetween Ranks 3 and 4, or among Ranks 5, 6, and 7. For example, groupscan be generated and if an RI is changed within a group, then the firstPMI can be used to calculate a second PMI and a CQI. RI groups aredefined as below.

Group 1: RI belongs to the set {1,2}

Group 2: RI belongs to the set {3,4}

Group 3: RI belongs to the set {5,6,7}

If a rank is changed from 2 to 3, or 5 to 4, then the first PMIindicates different wideband and long-term channel conditions. In thiscase, a certain pre-defined first PMI can be assumed to calculate thesecond PMI and the CQI, or the UE may not feedback (or may cancel) thesecond PMI and the CQI, as will be described below as another embodimentof the present invention.

The codebook structure of the 8 CSI-RS ports is as follow. The codebookstructure of the 8 CSI-RS port may use a codebook published in theR-105011 draft disclosed in the 3GPP website, and thus will not bedescribed in detail.

Case 1: Rank 1 and Rank 2

Codebook Expression: Rank 1 and Rank 2

The codebook is expressed as shown below.

$\mspace{20mu} {{B = \begin{bmatrix}b_{0} & b_{1} & \ldots & b_{31}\end{bmatrix}},{\lbrack B\rbrack_{{l + m},{l + n}} = ^{j\frac{2\pi \; m\; n}{32}}},\mspace{20mu} {m = 0},1,2,3,{n = 0},1,\ldots \mspace{14mu},31}$$\mspace{20mu} {X^{(k)} \in \left\{ {{{\begin{bmatrix}b_{2{kmod}\; 32} & b_{{({{2k} + 1})}{mod}\; 32} & b_{{({{2k} + 2})}{mod}\; 32} & b_{{({{2k} + 3})}{mod}\; 32}\end{bmatrix}\text{:}\mspace{20mu} k} = 0},1,\ldots \mspace{14mu},15} \right\}}$$\mspace{20mu} {W_{1}^{(k)} = \begin{bmatrix}X^{(k)} & 0 \\0 & X^{(k)}\end{bmatrix}}$ $\begin{matrix}{\mspace{79mu} {C_{1} = \left\{ {W_{1}^{(0)},W_{1}^{(1)},W_{1}^{(2)},\ldots \mspace{14mu},W_{1}^{(15)}} \right\}}} & {\langle{{Codebook}\mspace{14mu} 1}\rangle} \\{{{W_{2} \in C_{2}} = \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \right\}}\mspace{20mu} {Y \in \left\{ {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{4}} \right\}}} & {\langle{{Rank}\mspace{14mu} 1}\rangle} \\{\mspace{79mu} {{{W_{2} \in C_{2}} = \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}}{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{1}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{4},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{4}} \right)} \right\}}}} & {\langle{{Rank}\mspace{14mu} 2}\rangle}\end{matrix}$

In Ranks 1 and 2, {tilde over (e)}_(n) is a 4×1 selection vector withall zeros except for the n-th element with a value of 1.

Case 2: Rank 3 and Rank 4

Codebook Expression: Rank 3 and Rank 4

${B = \begin{bmatrix}b_{0} & b_{1} & \ldots & b_{15}\end{bmatrix}},{\lbrack B\rbrack_{{l + m},{l + n}} = ^{j\frac{2\pi \; {mn}}{16}}},{m = 0},1,2,3,{n = 0},1,\ldots \mspace{14mu},15$$X^{(k)} \in \left\{ {{{\begin{bmatrix}b_{4{kmod}\; 16} & b_{{({{4k} + 1})}{mod}\; 16} & \ldots & b_{{({{4k} + 7})}{mod}\; 16}\end{bmatrix}\text{:}k} = 0},1,2,3} \right\}$$W_{1}^{(k)} = \begin{bmatrix}X^{(k)} & 0 \\0 & X^{(k)}\end{bmatrix}$ $\begin{matrix}{C_{1} = \left\{ {W_{1}^{(0)},W_{1}^{(1)},W_{1}^{(2)},W_{1}^{(3)}} \right\}} & {\langle{{Codebook}\mspace{14mu} 1}\rangle} \\{{{W_{2} \in C_{2}} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}} \right\}}{\left( {Y_{1},Y_{2}} \right) \in \begin{Bmatrix}\begin{matrix}{\left( {e_{1},\begin{bmatrix}e_{1} & e_{5}\end{bmatrix}} \right),\left( {e_{2},\begin{bmatrix}e_{2} & e_{6}\end{bmatrix}} \right),} \\{\left( {e_{3},\begin{bmatrix}e_{3} & e_{7}\end{bmatrix}} \right),\left( {e_{4},\begin{bmatrix}e_{4} & e_{8}\end{bmatrix}} \right),}\end{matrix} \\\begin{matrix}{\left( {e_{5},\begin{bmatrix}e_{1} & e_{5}\end{bmatrix}} \right),\left( {e_{6},\begin{bmatrix}e_{2} & e_{6}\end{bmatrix}} \right),} \\{\left( {e_{7},\begin{bmatrix}e_{3} & e_{7}\end{bmatrix}} \right),\left( {e_{8},\begin{bmatrix}e_{4} & e_{8}\end{bmatrix}} \right),}\end{matrix} \\\begin{matrix}{\left( {\begin{bmatrix}e_{1} & e_{5}\end{bmatrix},e_{5}} \right),\left( {\begin{bmatrix}e_{2} & e_{6}\end{bmatrix},e_{6}} \right),} \\{\left( {\begin{bmatrix}e_{3} & e_{7}\end{bmatrix},e_{7}} \right),\left( {\begin{bmatrix}e_{4} & e_{8}\end{bmatrix},e_{8}} \right),}\end{matrix} \\\begin{matrix}{\left( {\begin{bmatrix}e_{5} & e_{1}\end{bmatrix},e_{1}} \right),\left( {\begin{bmatrix}e_{6} & e_{2}\end{bmatrix},e_{2}} \right),} \\{\left( {\begin{bmatrix}e_{7} & e_{3}\end{bmatrix},e_{3}} \right),\left( {\begin{bmatrix}e_{8} & e_{4}\end{bmatrix},e_{4}} \right)}\end{matrix}\end{Bmatrix}}} & {\langle{{Rank}\mspace{14mu} 3}\rangle} \\{{{W_{2} \in C_{2}} = \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}}{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{1}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{4},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{4}} \right)} \right\}}} & {\langle{{Rank}\mspace{14mu} 4}\rangle}\end{matrix}$

In Ranks 3 and 4, {tilde over (e)}_(n) is an 8×1 selection vector withall zeros except for the n-th element with a value of 1.

Case 1: Rank 5 to Rank 7

Codebook Expression: Rank 5 to Rank 8

$\begin{matrix}{\mspace{79mu} {{X^{(0)} = {\frac{1}{2} \times \begin{bmatrix}1 & 1 & 1 & 1 \\1 & j & {- 1} & {- j} \\1 & {- 1} & 1 & {- 1} \\1 & {- j} & {- 1} & j\end{bmatrix}}},\mspace{79mu} {X^{(1)} = {{diag}\left\{ {1,^{{j\pi}/4},j,^{{j3\pi}/4}} \right\} X^{(0)}}},\mspace{79mu} {X^{(2)} = {{diag}\left\{ {1,^{{j\pi}/8},^{{j2\pi}/8},^{{j3\pi}/8}} \right\} X^{(0)}}},\mspace{79mu} {X^{(3)} = {{diag}\left\{ {1,^{{j3\pi}/8},^{{j6\pi}/8},^{{j9\pi}/8}} \right\} X^{(0)}}}}} & \; \\{{{W_{1} \in C_{1}} = \left\{ {\begin{bmatrix}X^{(0)} & 0 \\0 & X^{(0)}\end{bmatrix},\begin{bmatrix}X^{(1)} & 0 \\0 & X^{(1)}\end{bmatrix},\begin{bmatrix}X^{(2)} & 0 \\0 & X^{(2)}\end{bmatrix},\begin{bmatrix}X^{(3)} & 0 \\0 & X^{(3)}\end{bmatrix}} \right\}},\mspace{79mu} {W_{2} = {\frac{1}{\sqrt{2}}\begin{bmatrix}{\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{3} \\{\overset{\sim}{e}}_{1} & {- {\overset{\sim}{e}}_{1}} & {\overset{\sim}{e}}_{2} & {- {\overset{\sim}{e}}_{2}} & {\overset{\sim}{e}}_{3}\end{bmatrix}}}} & {\langle{{Rank}\mspace{14mu} 5}\rangle} \\{{{W_{1} \in C_{1}} = \left\{ {\begin{bmatrix}X^{(0)} & 0 \\0 & X^{(0)}\end{bmatrix},\begin{bmatrix}X^{(1)} & 0 \\0 & X^{(1)}\end{bmatrix},\begin{bmatrix}X^{(2)} & 0 \\0 & X^{(2)}\end{bmatrix},\begin{bmatrix}X^{(3)} & 0 \\0 & X^{(3)}\end{bmatrix}} \right\}},\mspace{79mu} {W_{2} = {\frac{1}{\sqrt{2}}\begin{bmatrix}{\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{3} & {\overset{\sim}{e}}_{3} \\{\overset{\sim}{e}}_{1} & {- {\overset{\sim}{e}}_{1}} & {\overset{\sim}{e}}_{2} & {- {\overset{\sim}{e}}_{2}} & {\overset{\sim}{e}}_{3} & {- {\overset{\sim}{e}}_{3}}\end{bmatrix}}}} & {\langle{{Rank}\mspace{14mu} 6}\rangle} \\{{{W_{1} \in C_{1}} = \left\{ {\begin{bmatrix}X^{(0)} & 0 \\0 & X^{(0)}\end{bmatrix},\begin{bmatrix}X^{(1)} & 0 \\0 & X^{(1)}\end{bmatrix},\begin{bmatrix}X^{(2)} & 0 \\0 & X^{(2)}\end{bmatrix},\begin{bmatrix}X^{(3)} & 0 \\0 & X^{(3)}\end{bmatrix}} \right\}},\mspace{79mu} {W_{2} = {\frac{1}{\sqrt{2}}\begin{bmatrix}{\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{3} & {\overset{\sim}{e}}_{3} & {\overset{\sim}{e}}_{4} \\{\overset{\sim}{e}}_{1} & {- {\overset{\sim}{e}}_{1}} & {\overset{\sim}{e}}_{2} & {- {\overset{\sim}{e}}_{2}} & {\overset{\sim}{e}}_{3} & {- {\overset{\sim}{e}}_{3}} & {\overset{\sim}{e}}_{4}\end{bmatrix}}}} & {\langle{{Rank}\mspace{14mu} 7}\rangle} \\{\mspace{79mu} {{{W_{1} \in C_{1}} = \left\{ \begin{bmatrix}X^{(0)} & 0 \\0 & X^{(0)}\end{bmatrix} \right\}},\mspace{79mu} {W_{2} = {\frac{1}{\sqrt{2}}\begin{bmatrix}{\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{1} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{2} & {\overset{\sim}{e}}_{3} & {\overset{\sim}{e}}_{3} & {\overset{\sim}{e}}_{4} & {\overset{\sim}{e}}_{4} \\{\overset{\sim}{e}}_{1} & {- {\overset{\sim}{e}}_{1}} & {\overset{\sim}{e}}_{2} & {- {\overset{\sim}{e}}_{2}} & {\overset{\sim}{e}}_{3} & {- {\overset{\sim}{e}}_{3}} & {\overset{\sim}{e}}_{4} & {- {\overset{\sim}{e}}_{4}}\end{bmatrix}}}}} & {\langle{{Rank}\mspace{14mu} 8}\rangle}\end{matrix}$

In Rank 5 to Rank 8, {tilde over (e)}_(n) is a 4×1 selection vector withall zeros except for the n-th element with a value of 1.

In each case, the first PMI indicates the same matrix (W1), whichrepresents wideband and long-term channel conditions, respectively.

To prevent a situation where the calculation of the second PMI and theCQI becomes unclear, as described above, an H′ value, which is aperiodicity factor, may be restricted. The random value can cause thetime misalignment between an RI reporting period and a second PMI and aCQI reporting period.

Currently, reporting instances for an RI are subframes satisfyingEquation (1).

(10×n _(f) +└n _(s)/2┘=N _(OFFSET,CQI) −N _(OFFSET,RI))mod(H·N _(pd) ·M_(RI))=0  (1)

In Equation (1), the integer H is defined as H=J·K+1, and is related toa period in feedback transmission of the wideband second PMI. Thefeedback period of the wideband second PMI occurs in a period ofH·N_(pd) subframes. J indicates the number of bandwidth parts, and theparameter K is configured by higher-layer signaling. H includes a periodfor calculating a time taken in feeding back the wideband second PMI/CQIone time and repeating K times a process of feeding back the subbandsecond PMI/CQI for each bandwidth part. n_(f) is system frame number andn_(s) is slot number within a radio frame. The periodicity N_(pd) (insubframes) and offset N_(OFFSET,CQI) (in subframes) for CQI/PMIreporting are determined based on the parameter cqi-pmi-ConfigIndex(I_(CQI/PMI)) given in Table 7.2.2-1A in the 3GPP TS 36.213, v10.3.0.The value N_(OFFSET,RI) is the relative reporting offset for an RI.M_(RI) is a value related to a period of RI feedback transmission, andthe RI is fed back in a period of H·N_(pd)·M_(RI) subframes. That is, aperiod of feeding back the wideband second PMI/CQI M_(RI) times is equalto a period of feeding back the RI.

When the most recently transmitted PTI is 0, the wideband firstprecoding matrix indicator report has period H′·N_(pd), and is reportedon the subframes satisfying Equation (2).

(10×n _(f) +└n _(s)/2┘=N _(OFFSET,CQI))mod(H′·N _(pd))=0  (2)

In Equation (2), H′ is signaled by higher layers. H′ indicates theperiodicity factor, and is a value related to a period of the widebandfirst PMI, in which the period is H′·N_(pd).

If the value H′ is conditioned as H′=mH, 1≦m≦M_(RI), then even thoughthe RI is changed, the very next reporting time instance becomes firstPMI information. Therefore, when the PTI is not changed, there is nocase where the second PMI and the CQI do not have the proper first PMIinformation.

The UE does not feedback the second PMI and the CQI information when thelast reported RI is different from the RI condition, which the lastreported first PMI is calculated based on. More specifically, theerroneous feedback information of a second PMI and a CQI can cause thedegradation of system performance. The network (e.g., an eNB, a FemtoNode, etc.) can schedule the UE based on the second PMI and the CQI,which are calculated in the RI condition where the unclear first PMIinformation is generated. Accordingly, in this case, there is a highNegative ACKnowledgement (NACK) probability due to inadequate linkadaptation. Thus, according to the current embodiment, the method forreporting CSI in an uplink in a wireless communication system mayinclude not reporting the second PMI before reporting the first PMIbased on the changed RI, if the RI is changed before the second PMI isreported, after the first PMI is reported. The UEs not sending feedbackinformation help the system performance as in the current embodiment.

The benefit of this embodiment is two-folded.

This reduces the network interference level as the second PMI and CQIwithout the associated first PMI cannot be used by the network.

In the case of carrier aggregation, cancelling the second PMI and CQIreport on one Component Carrier (CC) can make room for a PUCCHtransmission on the other CCs.

A UE is prohibited from changing RI information under the above unclearreporting time condition. Consequently, as soon as an RI is reported,the next coming report is a second PMI and a CQI case. Although thismethod restricts UE behavior, all reporting information is valid fornetwork to support UE.

When the first PMI is not calculated based on the last reported RI, thenthe second PMI is calculated based on the first PMI and a correspondingprevious RI value, not based on the last reported RI.

FIG. 4 illustrates a method for calculating a second PMI based on aprevious RI condition according to an embodiment of the presentinvention.

Referring to FIG. 4, when an RI is changed at 405, and the nextreporting instance is the second PMI and the CQI reporting instance. Inthis case, in accordance with an embodiment of the present invention,the second PMI is calculated based on the first PMI at 403 and acorresponding RI value at 401, not based on the last reported RI at 405,until the new first PMI reporting time instance at 409. Therefore, thesecond PMI and the CQI at 409 are also calculated based on the first PMIat 403 and the corresponding previous RI preceding the change of the RIat 401. After the new first PMI is fedback at 411, the following secondPMI and CQI is calculated based on the first PMI at 411 and the lastreported RI at 405. The same procedure can be applied to the reportinginstance 413.

In the current embodiment, when the first PMI is not calculated based onthe last reported RI, then the second PMI and CQI are calculated basedon the first PMI, which is predefined in a cyclic method among thecandidate first PMI set of corresponding last reported RI.

For example, for this case, a certain first PMI set in Rank 2 may bedefined. It is assumed that this set includes first PMIs from index 0 to3 in the Table 6.3.4.2.3-4 in the 3GPP TS 36.211 v10.3.0. The first PMIis assumed in a cyclic way. Herein, the cyclic way indicates cyclicallyusing in an orderly manner predefined first PMIs among a plurality offirst PMIs in the candidate first PMI set. At the reporting instance407, the second PMI and CQI can be calculated based on the first PMIwith an index of 0. At the reporting instance 409, the second PMI andCQI can be calculated based on the first PMI of 1. At the reportinginstance 413, the second PMI and CQI can be calculated conditioned onthe first PMI with an index of 2.

FIG. 5 is a block diagram illustrating a UE according to an embodimentof the present invention.

Referring to FIG. 5, the UE that reports the CSI to the network andcalculates the second PMI and CQI under a predetermined conditionincludes an antenna 501, a transmitter 502 for reporting the CSI to thenetwork and a controller 503 for controlling operations of calculatingthe second PMI and CQI under the predetermined condition and reportingthe CSI.

While the present invention has been particularly shown and describedwith reference to certain embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes or modificationsmay be made therein without departing from the spirit and scope of thepresent invention as defined by the following claims and any equivalentsthereof.

What is claimed is:
 1. A method for reporting Channel State Information(CSI) in an uplink by a User Equipment (UE) in a wireless communicationsystem, the method comprising: reporting a first Precoding MatrixIndicator (PMI) to an evolved Node B (eNB); calculating a second PMIusing the first PMI; and reporting the second PMI to the eNB.